Compression question

[Fisherman550]

I have a 2001 Johnson, 2 stroke, 70 HP. Does anyone know what the cylinder compression should be? The motor really doesn't have a lot of hours for it's age.
Thanks in advance.

 

[Bubbakat]

The main thing about compression is that it be close to each other. No more then 10% difference in cylinders. I always like anything 100 and above but they will run at lower compression. They just don't run as good. The lower the compression the harder they are to start. After doing a compression check and its good I always do a leak down test that will tell the rest of the story. Hope this helps.

 

[wrechin2]

I agree with Bubbakat. BUT I would only worry about the leakage. That tells you the true health of the engine. Compression is not a good indicator. I have rebuilt many engine with good compression but will have a ton of leakage. Compression tells you that it can make pressure and a leakage test tells you if it can hold it. If it has high leakage, some the pressure of the air/fuel mixture burning is escaping and not pushing on the piston. This causes a power loss. Generally I find that the highest compression readings have the most leakage. This is due to carbon build up. Here is a prime example.

http://chattanoogafishingforum.com/forums/thread-view.asp?tid=44931&posts=2#M347677

This is the page out of a Johnson/Evinrude manual. Notice it says that IF the engine has EQUAL compression but is hard to start or performs poorly check for......... It is basicly telling you that you can have good compression and still have mechanical issues. A leakage test at 1/2 ATDC will tell you the whole story. Just my .02

 

[Fisherman550]

Thanks guys-that takes care of it.

 

[Oldman]

yeah what he said.